This invention relates to improved matrix printers. The invention relates more particularly to a printer which is adapted to print at variable character widths.
In one form of relatively high speed printing device, a character printing head is transported parallel to a stationary platen and is repeatedly accelerated in a transverse direction toward the platen. The printing head forms characters on the medium during the transport.
One form of relatively high speed printer comprises a dot matrix printer. In dot matrix printing, a character is formed by a plurality of printed dots which are selected from a rectangular array or matrix of dot locations arranged in columns and rows. The printing head in one form of dot matrix impact printer includes a plurality of individually selectable print wires which are aligned to form one or more of the dots of a matrix column. These print wires are accelerated toward the platen by associated solenoids at a matrix column location to cause printing on a record medium through an inked ribbon. Scanning of the head along the platen results in the successive columnar printing of additional dots necessary to form the characters at successive matrix locations.
The printing of a plurality of characters along a line requires that the position of the head be monitored and controlled. In dot matrix printing for example, the position of the array of print wires with respect to a dot matrix column should be established. To this end, head position encoders have been utilized which establish the desired positions along the platen of the dot matrix columns. This has been accomplished in one arrangement by utilizing an optical sensing system for measuring relative movement between the printhead and the stationary platen. In a particular optical sensing system, a circular disc having a plurality of incremental reference indicia, for example, lines or slits, formed thereon is mechanically coupled to a printhead drive motor. A stationary optical sensor is positioned adjacent the disc and radiant energy, which is projected from a source through incremental reference slits of the disc, causes the sensor to generate electrical signals representative of the position or printing positions and thus of the dot matrix columns to be printed. An alternative optical sensing arrangement utilizes a linear encoder instead of a rotating disc, linear fixed reference marks and an optical sensor which is mechanically coupled to and transported with the moving printhead. In either case, incremental reference signals are generated which are utilized for locating dot matrix columns of a dot matrix character.
The reference or position incremental signal has been utilized in several ways for locating the dot matrix column. In one arrangement, a reference incremental signal is generated which corresponds to each dot matrix column to be formed so that the signal itself is representative of the location of the dot matrix column. In another arrangement, a reference incremental signal is sensed at the location of an initial dot matrix column of a character. The printhead advances at a relatively constant printhead velocity and successive dot matrix column locations within the character are determined by timing the movement of the printhead with respect to the initial column. In still another arrangement, multiple encoder tracks are employed for separately sensing the initial and terminal locations of matrix columns of a dot matrix character.
The above-described matrix column location sensing arrangements provide for sensing the locations at a particular character density. For example, a presently utilized examplary character density is ten characters per inch. At times, it is desirable to increase the character density to relatively larger densities on a page. Character density can greatly be changed by varying the width of a character. Character width variation requires that spacing between adjacent dot matrix columns of a character be relatively changed. The reference incremental signals described hereinbefore are unsuitable to accommodate alternative printing at different character widths. In prior arrangements, the drive system was physically modified in order to provide for different character widths. For example, a drive wheel or gear was substituted in order to change the matrix column spacing for a character of different character width. Alternatively, an encoder disc was provided which included a plurality of reference tracks having reference lines and wherein each of the tracks was related to a particular character width.
The prior art arrangements for determining matrix column locations for different character widths exhibit several disadvantages. With gear or wheel changing, the operation of the printer is dedicated to a single character width. Relatively complex and costly circuit arrangements are required in the case of the encoder discs having multiple tracks.
Accordingly, it is an object of this invention to provide an improved matrix printer which is adapted to print at different character densities.
Another object of the invention is to provide an improved matrix printer having relatively non-complex and economical means for printing at a plurality of different character widths.
Another object of the invention is to provide an improved impact printer adapted to mix characters of different character widths.
A further object of the invention is to provide an improved means, including an encoder disc, for printing characters at different character widths.